Processes for the preparation of di-carboxylic acids are known to produce crude mixtures containing various on-path and off-path carboxylic acids. Various waste streams from other processes may also contain di-carboxylic acids. Thus, separation of these mixtures and streams is necessary in order to obtain a sufficiently pure product or recover useful fractions of waste streams containing di-carboxylic acids. Methods for the separation and purification of carboxylic acids have been disclosed (See, for example, U.S. Pat. No. 6,284,904, U.S. Patent Application Publication No. 2013/0345473; J. Chromatogr. A. 850, 1999, p 187; J. Chromatogr. 57, 1971, p 353; J. Chromatogr. 253, 1982, p 87). Several of the methods disclosed in the art describe the use of anion exchange column chromatography with particular eluents such as organic acids (e.g., acetic acid or formic acid), bases (e.g., sodium bicarbonate or sodium tetraborate), and strong acids (e.g., sulfuric acid or hydrochloric acid).
Although industrial chromatographic separation methods are one approach for the separation of mono-carboxylic acids and di-carboxylic acids, the use of strong acids, organic acids, bases or eluent components other than water that may be necessary to produce an effective separation and elution is not desirable. These additional components increase reagent costs and may require disposal if recovery is not possible after use. Further, these additional components may necessitate additional equipment for removal and recovery after use, which increases process costs. Accordingly, there remains a need for an industrially advantageous separation process in which the eluent does not introduce extraneous components into process streams. Further, in processes for the production of di-carboxylic acids in which the reaction solvent is water, there remains a need for an industrially advantageous separation process in which water can be used as the primary eluent to facilitate the separation and elution of di-carboxylic acids from other components present in a crude reaction mixture.
Moreover, in processes for preparing di-carboxylic acids, such as in the oxidation of glucose to glucaric acid as described in U.S. Pat. No. 8,669,397 and oxidation of a pentose to pentaric acid (e.g., xylose to xylaric acid) as described in U.S. Pat. No. 8,785,683, which are incorporated herein by reference, there remains a need for efficient and cost effective separation techniques for the desired di-carboxylic acid to facilitate improved process yields and economics.